Recovery of chlorine from gaseous mixtures



Feb. 17, 1942. El, MUSKAT 2,273,723

RECOVERY OF CHLORINE FROM GASEOUS MIXTURES Fi'led April 14, 1939 Na OH ICHLoRmE OR zco DLiiENT Cl C12,

4- rnLuEn-r l H1O 01 DILUENT HO C1 7 SOLUTION CYILOQ PURE o3 INVENTOR.lRvma E. MusKA'r Patented Fe-b. 17,1942

amen STATES. PATENT" oFFlcg 4 I a y Y Q nacovnar on zaz l mm GASEOUS yFeb. 15, 1938, and 216,475, filed June 29, 1938,

Pa, acorporation of Pennsylvania 'Applica'tion April 14, 1939,;SerialNo. 267,917

12'Claims. (c1.23 145) This'inventionrelatestoa method of recoveringchlorine in concentrated form from, chlorine mixtures which containsubstantial amounts of other, gaseous agents. It has long beenrecognized that a cheap economical method .of recovering 5 chlorine fromother gases is desirable. Numerous reactions involving the use ormanufacture of chlorine or chlorine compounds result in the productionof chlorine gas which is greatlyv diluted with other gases such as air,nitrogen, oxygen, carbondioxide or other gas which is normally insolublein water. This is particularly true when various metallic chlorides suchas iron,

titanium, chromium, aluminum orsilicon chlorides arethermally decomposedin air to form the corresponding oxides. The chlorine concentrationresulting from such a process is .often below 50 percent by volume andoccasionally is as low as 5-10 percent. g r V Various processes havebeen suggested for the recovery of this chlorine. Attempts have beenmade to recover it by means of liquefaction processes. While this can bedone, extensive compressing and refrigerating equipment is required 2and the process is uneconomical. Attempts to "extract the chlorine bymeans of solvents often ,In order to convert the dilute chlorine tochlo- 4 rine monoxide, the gaseous mixtures mayv be I contacted with .asuitable agentsuchas active mercuric oxide or an alkaline alkali metalcoma pound such as sodium hydroxide, sodium car- I bonate, sodiumbicarbonate, etc. Details of processes suitable for this purpose may befound in copending applications Serial No. 136,802, 136,803,

and 136,804 filed April 14,1937, No. 190,618, filed now Patents Nos.2,155,281; 2,157,558; 2,157,559; 2,157,524 and 2,157,525 respectively.Other suitable methods forfproducingwchlorine monoxide may be used. Theaccompanying drawing diagrammatically illustratesa suitable method ofapplication of the process herein described.

v The proportion of chlorine monoxide produced in a single treatment isdependent upon the 'Irnethod of treatment.

When active mercuric oxide is used, substantially the entire quantity ofchlorine in'the gas'ma'y be converted into chlorine monoxide, ifdesired. On'the other hand, where sodium carbonate or similar agent isused, the percentage conversion of chlorine monoxide is found to besubstantially lower. In some cases it may be desirable to convert only aportion of the chlorine into chlorine monoxide and to use an excess ofchlorine even when mercuric oxide is used for the conversion in order toinsure complete utilization of this agent with maximum efflciency and toavoid explosive concentrations of chlorine monoxide. In such a casea'rnixture containing chlorine and chlorine monoxide is secured. In theusual operation of this process using agents such as sodium carbonatefor the conversion, less than percent of the chlorine is converted intochlorine monoxide and in general the conversion is below 40 percent ofthe chlorine.

The resulting gaseous mixture containing chlorinemonoxide may then betreated for the recovery of chlorine monoxide. In accordance with oneeffective method of recovering the chlorine monoxide, the gaseousmixturemay be contacted with a suitable solvent such as water or carbontetrachloride. By limiting the amount of water used, it is possible torecover substantially all of the chlorine monoxide without dissolving anappreciable amount of chlorine.

Thepresence of the other inert gases exerts a noticeable depressingeffect upon the solubility of chlorine andserves to substantiallyminimize any tendency for the chlorine to dissolve. This is particularlytrue when the amount of water used is limited to permit the formation ofhypochlorous acid having a concentration in excess of 5 vpercent, sincethe solubilityv of chlorine in such a solution is somewhat lower thanthe solubility in water. For this reason it is 'desiredto regulate'theamount of water used in order toform a solutionhaving a' concentrationof HOCI in excess of 5 percent by weight. After removal of the chlorinemonoxide the gases maybe recirculated for further production of chlorineI monoxide.

The hypochlorpus acidthus obtained is found to be ofhigh purity andcontains only minor quantltiesof chloride and chlorate. Uponcontactingthis acid with a compound which is capable of being" oxidized byhypochlorous acid, such as the lower metallic oxides or the metallicinvention.

a vam I content of this solution was less than 0.3 percent.

110 parts by weight of the solution was mixed with parts by weight ofchromic oxide at a temperature of 90 C. and chlorine was evolvedimmediately in avigorousreaction. The chlorine upon collection and afterremoval of moisture was 99 percent pure. 7

tion of chlorine and chromic acid. Thus, this v process is effective inproducing both chromic acid and chlorine in recoverable form. Whenchromic acid is generated by contacting lower oxides of chromium withhypochlorous acid as generally prepared, containing a substantialquantity of chloride ion, it is diflicult'to recover the chromic aciddue to thepresence of a substantial amount of chloride ion. This iongenerally exists in present grades of hypochlorous acid. .The separationof chloride from chromic acid is very diflicult since the chloride tendsto react with the chromic acid when attempts are made to isolate theacid. Since the hypochlorous acid prepared as set forth herein issubstantially free from chlorides, containing less than 3 grams perliter of this material, the recovery of chromic acid in V substantiallypure form by evaporation is relatively simple.

Other oxidizable oxides such as stannous, oxide ance with thisinvention. Similarly oxidizable metals such as iron, or aluminum, oroxidizable chlorides such as hydrochloric acid'or the chlorides ofsodium, potassium, copper, zinc, calcium, magnesium, lithium or chromiumor'other metallic chloride. V

In treating with hypochlorous acid it is preferred to apply heat to thesolutions in order to stimulate the rate of reaction and to securehigher yields. Temperatures in excess of 50 C. are found to bedesirable.

The process is of particular value in the recovery of chlorine fromgases resulting from processes involving the thermal decomposition ofmetallic chlorides. Thus, in the manufacture of titanium dioxide, it isoften desirable to decompose titanium tetrachloride or similar halidewith air. This process usually results in the formation of a gaseousmixture containing but percent by volume of chlorine, the balance beingnitrogen and other inert gases. A similar mixture is produced uponthermal decomposition of chromic or chromous chloride or ferricchloride. The process may also be adapted to the recovery of chlorinefrom exhaust gases from electrolytic cells.

' The following example is illustrative of the A quantity of chromicchloride was heated at a temperature of 500 C. in a stream of airwhereby chromic oxide was formed and a gaseous .mixture containing 30percent by volume of chlorine and the balance oxygen and nitrogen wasobtained. This gaseous mixture was coun- In the preparation of chlorinemonoxide by interaction of chlorine and-an agent such as mercuric oxideor an alkaline alkali metal compound such as sodium carbonate, aquantity of chlorine may be utilized in the formation of thecorresponding metal chloride. If desired, the hypochlorous acid producedmay be used to decompose these chlorides to release and recover thechlorine so consumed.

Although the present invention has been described with reference to thespecific details of certain embodiments thereof, it is not intended thatsuch details shall be regarded as limitations upon the scope of theinvention except insofar,

as included in the accompanying claims.

I claim: 1. A method of recovering chlorine from a gaseous mixture whichis derived from a process which results in the formation of a gaseousmixture containing chlorine and a' substantial amount of other gaseousconstituents which are normally insoluble in water which comprisestreating the mixture to convert at least a substantial portion of thechlorine into chlorine monoxide, contacting the mixture with a quantityof water whereby the major portion of the chlorine monoxide is absorbedwithout absorption of a substantial amount of said gaseous constituents,and a solution of hypochlorous acid is produced, contacting thehypochlorous acid with an oxidizable material which is capable ofreducing hypochlorous acid to generate chlorine andrecovering thechlorine.

2. A method of recovering chlorine from a gaseous mixture which isderived from a process which results in the formation of a gaseousmixture containing chlorine and a substantial amount of other gaseousconstituents which are normally insoluble in water which comprisestreating the mixture to convert at least a substantial portion of thechlorine into chlorine monoxide, contacting the mixture with a quantityof water whereby the major portion'of the chlorine monoxide is absorbedwithout absorption of a substantial amount of said gaseous constituents,and a solution'of hyochlorous acid is produced, contacting thehypochlorous acid with an oxidizable metallic oxide which is capableofreducing hypochlorous acid to generate chlorine and recovering thechlorine.

3. A method of recovering chlorine from a gaseous mixture whichisderived from a process which results in the formation of a gaseousmixture containing chlorine and a substantial amount of other gaseousconstituents which are normally insoluble in water which comprisestreating the mixture to convert at least a substantial portion of thechlorine into chlorine monoxide, contacting the mixture with a quantityof water, whereby the major portion of the chlorine monoxide is absorbedwithout absorption of a substantial amount of said gaseous constituentsand a solution of hypochlorous acid is produced, contacting thehypochlorous acid with anoxidizable chromium oxide which is capable ofreducing hypochlorous acid to generate chlorine and recovering thechlorine.

4. A method of recovering chlorine from a gaseous'mixture which isderived from a process ture. containing chlorine and a substantialamount of other gaseous constituents which are normally insoluble inwater which comprises treating the, mixture to convert at least asubstantial portion of the chlorine into chlorine .monoxide, contactingthe mixture with a quantity of water whereby the major portion of thechlorine monoxide is absorbed without absorption of a substantial amountof said gaseous constituents, and a solution of hypochlorous acid i 5. Amethod of'recovering chlorine from a gaseous mixture which is derivedfrom a process which results in the formation of a gaseous mixturecontaining chlorine and a substantial amount of other gaseousconstituents which are r fwhich results in the formation of a gaseousmixnormally insoluble in water which comprises treating the mixture toconvert at least a substantial portion of the chlorine into chlorinemonoxide, contacting the mixture with a quantity of water, sufiicient toabsorb the major portion of the chlorine monoxide but insuiilcient toabsorb an appreciable amount of chlorine whereby a solution ofhypochlorous acid isproduced recycling the unabsorbed chlorine,contacting the hypochlorous acid with a chromic oxide which is capableof reducing hypochlorous acid to generate chlorine and recovering thechlorine.

6. A method of recovering chlorine from a gaseous mixture which isderived from a process which results in the formation of agaseousmixture containing up to about 50 percent of chlorine and asubstantial amount of other gaseous constituents which are normallyinsoluble in water' which comprises treating the mixture to convert atleast a portion of the chlorine into chlorine monoxide, contacting themixture with a quantity of water, suflicient to absorb the major portionof the'chlorine monoxidebut insuflicient to absorb an appreciable amountof chlorine.

whereby a solution of hypochlorous acid is produced recycling theunabsorbed chlorine, contacting the hypochlorous acid withanoxidizable,v

material which is capable of reducing hypochlorous acid to generatechlorine and recovering the chlorine. i

'7. A method of recovering substantially pure chlorine which comprisesdecomposing a metallic chloride in air at a temperature sufficientlyhigh 7 to cause evolution of chlorine in admixture with nitrogen,treating the mixture to convert at least a substantial portion of thechlorine into chlorine monoxide, contacting the mixture with a quantityof water, whereby the major portion of the chlorine monoxide is absorbedwithout ab- 60 sorption ofa, substantial amount of said gaseousconstituents, and a solution of hypochlorous acid is produced,contacting the hypochlorous acid with an, oxidizable material which iscapable of reducing hypochlorous acid to generate chlorine andrecovering the chlorine.

8. A method of recovering chlorine from a gaseous mixture containing thesame which comprises treating the mixture to convert at least a portionof the chlorine into chlorine monoxide, contacting the mixture withsufficient water to dissolve the chlorine monoxide, treating theresulting solution with an oxidizable material which is capableofreducing hypochlorous acid, whereby chlorine is liberated and recoveringthe liberated chlorine.

9. A method of preparing chromic acid and chlorine which comprisescontacting a solution of hypochlorous acid, which is substantially freefrom chloride ion, with, a lower oxide of chromium.

10. A method of preparing chromic acid and chlorine which comprisescontacting a solution of hypochlorous acid which is substantially freefrom chloride ion, with a lower oxide of chro-- convert up to 40 percentof the chlorine to chlorine monoxide and to form a gaseous mixturecontaining chlorine and chlorine monoxide, contacting the resultingmixture with a 7 limited quantity of water suificient to absorb themajor portion of the chlorine monoxide but insufficient to absorb an apreciable amount of chlorine whereb a, solution of hypochlorous acid isforme recycling unabsorbed chlorine, contacting the hypochlorous acidwith a material capable of reducing hypochlorous acid to generatechlorine, and recovering the chlorine.

12. A method of recovering chlorine from a gaseous mixture containingnot in excess of percent chlorine and a substantial quantity of othergaseous constituents which ar not soluble in water which comprisestreating the mixture to convert up to '75 percent of the chlorine tochlorine monoxide and to form a gaseous mixture containing chlorine andchlorine monoxide, con-v tacting the resulting mixture with a limitedquantity of water sufficient toeabsorb the major whereby a solution ofhypochlorous acid is I formed, recycling unabsorbed chlorine,contacting' the hypochlorous acid with a material capable 'of reducinghypochlorous acid to generate chlorine and recovering the chlorine.

' IRVING E. MUSKAT.

